1. Field of the Invention
The present invention relates to a two-part room temperature curable composition which can be used widely in various fields such as adhesives, coating materials, gap-filling materials and casting materials.
2. Description of the Prior Art
As a two-part curable composition, there is known a two-part radically-polymerizable composition mainly containing a radically-polymerizable acrylate (or methacrylate) monomer. Moreover, one part of the known composition further contains organic peroxides as polymerization initiators, while the other part thereof contains, for example, metal chelate compounds, organic amines, carboxylic acids, polyamides, organic phosphorus compounds, thiourea compounds or metal salts, as polymerization accelerator. Generally, such a two-part radically-polymerizable composition is excellent in the rapid curing property and low temperature curing property as well as in the workability. Therefore, if used for adhesion or protective coating of parts or components constructing cars, speakers, small-size motors and other electric machines, the two-part curing composition can be expected to enhance the productivity of these articles.
In most cases, for giving surface-drying ability to the adhesive, a volatile monomer such as methyl methacrylate is used as the radically-polymerizable monomer to be contained mainly in the composition. However, such an acrylate (methacrylate) monomer is extremely hard and presents relatively large curing shrinkage in general.
To improve these drawbacks, various methods have been considered so far, in which for example many kinds of organic polymers (e.g., various synthetic rubbers or synthetic resins) ore added to the composition. However, even in such methods, the above-mentioned problems still remain to be solved. Namely, in case of filling adhesion or in cases where the adhered portion must experience low and high temperature conditions repeatedly, relatively large curing shrinkage still occurs and results in warpage. Thus, the portion to be adhered by such a composition is likely to be worn or broken under such conditions.
Also in the field of epoxy-type curable compositions, there are known methods based on addition of various kinds of rubber or modification of main or side chains of an epoxy compound with urethane or other rubber-related groups in order to make these compositions soft and flexible.
Recently, compositions comprising combination of modified silicone, an epoxy resin and a known epoxy-resin curing agent have been proposed as compositions presenting elasticity virtually equivalent to rubber. The compositions of this type are used for easing warpage or stress of a portion to be adhered by the compositions. Namely, the physical properties of the adhesives are utilized to lessen the stress to be caused by repetition of low and high temperature conditions and therefore to enhance much the reliability or durability of adhesion.
However, though the silicone-epoxy compositions have such excellent properties as mentioned above, the curing rate of the compositions is generally low at ordinary and low temperature conditions. Therefore, such silicone-epoxy compositions must be restricted from use in an assembly line or coating process which requires rapid curing.